Semiconductor image sensor array device, apparatus comprising such a device and method for operating such device

ABSTRACT

A plural line CMOS sensor array device is provided with sensor cells arranged in a matrix of coordinate-wise rows and columns. Each cell comprises a photosensitive area, an output node, and a transfer gate for selectively interconnecting the photosensitive area and the output node. Along at least a first coordinate direction adjacent cells are functionally configured as mutually mirror-symmetric structures in that their proximate output nodes are facing each other and are arranged for separately feeding a respective output channel. Preferably, also in a second coordinate direction adjacent cells are functionally configured as mutually mirror-symmetric structures in that their proximate output nodes are facing each other and all such facing output nodes are separately feeding a respective column-directed output channel.

This application is a divisional application of, and claims priorityfrom, U.S. Ser. No. 12/378,236 filed Feb. 13, 2009 (now U.S. Pat. No.8,119,967, granted Feb. 21, 2012), which is a divisional application ofand claims priority from U.S. Ser. No. 11/806,605 filed Jun. 1, 2007.

BACKGROUND OF THE INVENTION

The invention relates to a plural-line CMOS semiconductor image sensorarray device provided with sensor cells arranged in a matrix ofcoordinate-wise rows and columns, each cell comprising a photosensitivearea, an output node, and a transfer gate for selectivelyinterconnecting the photosensitive area and the output node, as beingrecited in the preamble of claim 1.

Such sensor arrays will represent useful tools for various types ofimaging purposes, such as medical, hand-held telephone, surveyance andvarious others. Basically, there are two prime technologies, CCD andCMOS. Although both have particular pluses, the present inventionfocuses on CMOS cells. In particular, CMOS has a markedly lower noisepotential for high-speed imaging. Furthermore, CMOS does not necessitatea noise versus bandwidth trade-off, since there can be multiplelow-speed analog signal chains provided within a single CMOS die. It isto be noted that in this application CMOS means (C)MOS which impliesthat the semiconductor imaging sensor array device is based on CMOS(=Complimentary Metal Oxide Semiconductor) technology or on NMOStechnology or on PMOS technology. In CMOS technology, which relates tothe preferred embodiments, both NMOS and PMOS technology is used.

The present invention provides various aspects of use for plural-linesensor by having neighboring cell rows and columns lying close togetherwithout intervening gap strips other than necessary for electronicseparation between neighbor rows and columns. By providing a limitedamount of control circuitry within the cell area, flexibility of controlwill greatly be enhanced. This local circuitry may advantageously becombined with overall control facilities and/or separate dataconnections for the cells.

Furthermore, the invention does away with geometrical shift (notably ahorizontal half pixel shift) between one array row and its next neighborinasmuch as the present format would allow for various advantages bothin design and operating of the array

By itself, U.S. Pat. No. 6,566,697 B1 published May 20, 2003, thatshares one inventor with the present patent application and has beenassigned to the present Assignee, discloses a PINNED PHOTODIODE FIVETRANSISTOR PIXEL that can be used as a pixel building block for thepresent arrangement. In view of the prior art's extensive circuitrydisclosure, the present text will consider most electronic signalaspects as being obvious to persons of average skill in the CMOS designart.

Furthermore, US Publication 2006/0284177 A1 published on Dec. 21, 2006,discloses a solid state image sensor with row-shared photodiodes. Thepresent invention allows for a raised flexibility.

SUMMARY TO THE INVENTION

In consequence, amongst other things, it is an object of the presentinvention to configure an array device as recited in order to allowexecuting various different operating modes through measures that aretaken inside or proximate to the array.

Now therefore, according to one of its aspects, the invention ischaracterized according to the remainder part of claim 1. In particular,the mirror symmetry aspect pertains to the position of the output node.Regarding various design considerations, the orientation of the transfergates, and/or the detailed shape of the output node area can have somedeviation from exact mirror symmetry. Generally control parts areconcentrated in a corner area of the pixel. This allows for sharingvarious elements among neighboring pixels.

Advantageously, transfer gates pertaining to output nodes so facing eachother are arranged for being either collectively actuated or,alternatively, for being actuated odd gates mutually exclusive withrespect to even gates, and vice versa. For one, this allows for separatecontrol between odd and even rows of a multi-row array.

Advantageously, also in a second coordinate direction adjacent cells arefunctionally configured as mutually mirror-symmetric structures in thattheir proximate output nodes are facing each other and all such facingoutput nodes are separately feeding a respective column-directed outputchannel. The same geometrical caution as above applies also here, butthe design and operation of the array will be facilitated appreciably.One aspect of the control would pertain to so-called binning, whereinsignals of adjacent cells are joined to apparently produce a larger cellarea. Although the combining of two cells will only lead to a √2improvement in dynamic range, the disadvantage of this relatively weakerimprovement can be offset by the lower noise potential of CMOS for highspeed imaging.

Advantageously, also in said second coordinate direction odd and eventransfer gates are arranged for being either collectively actuated or,alternatively actuated odd gates mutually exclusive with respect to evengates, and vice versa. This completes a set of operational modes, inparticular the discriminating between various pixel rows.

The invention also relates to an apparatus comprising a sensor arraydevice as recited supra and to a method for operating such sensor arraydevice. Persons skilled in the art will from the disclosure hereinreadily grasp implementations for such use of the inventive principle.Further advantageous aspects of the invention are recited in dependentClaims.

Particular advantageous aspects of CMOS technology as compared with CCDtechnology for line scan application are:

-   -   Higher line rate with a larger number of pixels    -   Higher line rate with a dual linescan structure    -   Closer spatial separation between colors    -   For a given line rate, lower noise is expected to be attained

Particular advantageous aspects of the architecture herein are asfollows:

-   -   Instead of one line of pixels in a linescan, use plural        linescans, especially two or four; some highly specialized        arrays could use eight lines, although this number is not an        express limitation; the prime usage is expected for four-line        arrays; in particular, plural lines can scan the image multiple        times, which results in a better signal to noise ratio    -   Independent global shutter for each line of pixels    -   Adjacent pixels can be binned in a 2×2 format    -   Minimized crosstalk between lines

From a control point of view, the following advantageous aspects apply:

-   -   The exposure control gate controls the start of the integration        time    -   The transfer gate controls the end of the integration time    -   All pixels in the same row have exposure control and transfer        gates connected together    -   Different rows have different exposure control and transfer        gates    -   The arrangement allows independent row-to-row control of        integration start and end times    -   Binning gates can be used to select between 2×2 binning or        no-binning modes

BRIEF DESCRIPTION OF THE DRAWING

These and further features, aspects and advantages of the invention willbe discussed more in detail hereinafter with reference to the disclosureof preferred embodiments of the invention, and in particular withreference to the appended Figures that illustrate:

FIG. 1, a single row of sensor cells, wherein odd cells have theirreadout nodes at lower right, and even cells have their readout nodes atlower left;

FIG. 2, an arrangement of four adjacent sensor cells in two rows and twocolumns;

FIG. 3, row-wise successive blocks of four adjacent sensor cells;

FIG. 4, a block-wise arrangement of 4×4 cells;

FIG. 5, an arrangement for use as a color linescan only;

FIG. 6, a high-resolution small pixel arrangement;

FIG. 7, a further high-resolution small pixel arrangement;

FIG. 8, a low-resolution large pixel arrangement.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates a single row of sensor cells, wherein odd cells havetheir readout nodes at lower right, and even cells have their readoutnodes at lower left. Generally, odd and even neighbor cells are mirrorsymmetric. In the arrangement shown, photosites 21 cover relatively thegreatest part of the cell area. They are connected by means of transfergates 25 to readout nodes 22. Each readout node 22 is connected througha respective output channel 30, 32 to an output facility of the sensorcell array. Finally, item 23 represents the binning gates that allow tocombine the output signals of the left and right sensor cell pairs inthe Figure. For simplicity, functionally corresponding elements carrycorresponding reference numerals throughout the disclosure. Thearrangement can be modified to some extent. For example, some or alltransfer gates 25 may connect Northward in the Figure instead of East orWest. This could also be combined with a slightly different form ofeither photosites and/or output nodes. Even so, the overall geometry ofthe cells has an odd/even mirror symmetry character. Expressly throughproviding this symmetry, the joining and/or selecting of controlfacilities and data connections will be made possible. A plural linesensor array cell device can now be produced by repeating the cell rowsshown in FIG. 1 as many times as considered feasible. A preferredembodiment will however be disclosed with respect to the further Figureshereinafter. Note that pixels are represented as square areas. However,they could be rectangular with unequal sides.

FIG. 2, illustrates an arrangement of four adjacent sensor cells in tworows and two columns. The upper two cells substantially repeat thearrangement of FIG. 1. The lower two cells are in mirror symmetry bothwith each other and also with the upper two cells, with similar cautionas discussed with regards to FIG. 1. Additionally, the lower two cellshave transfer gates 24: through separate control among output gate pairs24, 25 either the bottom row or the top row can be controlledseparately, or rather combined. Each of the four output nodes 82, 84,86, 88 feeds a separate output lead running downwards in the Figuretowards circle area 34. For clarity, the content of this circle area 34has been shown in an enlarged manner at lower right. The output nodesare each connected to amplifier source follower FETs 81 and 83. Theenabling of MOS gates 9 will connect the signals from the bottom row ofcells to the analog chains 36 and 38, whereas the enabling of MOS gates10 will connect the signals from the top row of cells. Finally, item 90represents binning gates that allow to combine the output signals of theleft and right sensor cell pairs in the Figure. Likewise, item 92represents binning gates that allow to combine the output signals of theupper and lower sensor cell pairs in the Figure. Therefore, the controlarrangement as shown allows to output either separate cells of the upperversus the lower row, the separate combining of left and right column,respectively, or the combined outputting of all four cells.

Note that amplifier FETs 81 and 83 and row switch gates 9 and 10 can belocated in the pixel itself, along with an associated amplifier notshown for brevity. In a device drawing for IC processing, they could fitbetween the binning gates (23), but also in the middle of the Figure.The row switch gates and the amplifier do need be laid out with anysymmetry restrictions.

FIG. 3 illustrate row-wise successive blocks each of four adjacentsensor cells. Next to the features shown in FIG. 2, and whilstsuppressing the output facilities 9, 10, 36 and 38, 81, 83, items 26 and27 represent the exposure control gates for the lower and upper rows,respectively. Finally, items 28 represent the exposure control's drainelectrodes. For clarity, the control and powering connections forvarious gates have not been shown particularly. Indeed, persons skilledin the art of integrated circuit CMOS design will readily conceiveappropriate layouts for such connections.

FIG. 4 illustrates a block-wise arrangement of 4×4 cells. Largely, thelayout is in mirror symmetry between the upper two and lower two rows ofcells. The upper two rows will output to the upper side of thearrangement and the power two rows ditto to the lower side. Thecombining or binning gates 90, 92, 94 and 96; the transfer gates 24, 25,34 and 35; and the exposure control gates 26, 27, 37 and 39 are separatefrom each other for the upper and lower row pairs, respectively.

Hereinafter, various applications for the arrangements, supra, will bediscussed. Generally, the prime layout will have four rows of cells; forparticular applications, eight rows of cells may be useful, taking intoaccount that a raised number of output lines (for example, 36 and 38 inFIG. 2) will mean additional substrate area required for these lines andtherefore, a smaller available area for light collection.

Now, FIG. 5 illustrates an arrangement for use as a color linescan only.If this is the only envisaged field of use, each of the four rows 40,42, 44, 46 may get its own spectral filter as symbolized with arespective different shading level. This feature allows RGB andmonochrome readout independently. Advantageously over CCD technology,this design allows close spacing between colors and generates low noiseat high line rates.

Other filter patterns can be considered as well, next to having each rowassigned to a particular single color. For example, each row can have auniformly rotating spectral sequence, such asred-blue-green-red-blue-green, etcetera. Various pattern recipes havebeen produced in literature.

FIG. 6 illustrates a high-resolution small pixel arrangement. One schemeinvolves the readout of top and bottom lines 48 and 54 only (lightshading) whilst discarding the remainder two lines 50 and 52. By way ofrefinement, fault correction can be effected as follows. If one of thepixels is corrupted by background radiation or otherwise, it can bereplaced by the other pixel (row 4 cell replacing row 1 cell and viceversa). Contrariwise, if neither pixel is corrupted, combining their twosignals by averaging will provide a 42 increase in dynamic range. Theabove feature of correcting does not require a rescan and in thereforeboth simple and fast. Neither would a redundant sensor be required. Bothalternatives would be relatively expensive.

FIG. 7 illustrates a further high-resolution small pixel arrangement.Here, all four cell rows 56, 58, 60, 62 are used. Moreover, with greatercamera complexity the usage, i.e. the combining of all four rows allowsa 2 times increase in dynamic signal range.

FIG. 8 illustrates a low-resolution large pixel arrangement with fourlines 64, 66, 68, 70. Various organizations are feasible. The first isbinning by four 2×2 pixels for a two times linear increase of pixelsize. Binning is useful in situations when the imaging system requires alarger pixel to collect more light from the object, or when a fasterscan through the readout of fewer pixels is required. Another field ofuse is to treat two binned rows as dual linescans for √2 times increaseddynamic range. In addition, the low noise and high line rate of CMOSwill produce at least a like quality level as compared to CCD.

Hereinafter, various policies will be described for improving signalquality when influenced adversely by one or more of backgroundradiation, other random background events evolving outside the sensordie, such as electrical glitch or magnetic interference, deviationsthrough internal defects and events within the sensor physicalstructure, and various others. The effect of such defects on aparticular signal can be pixels that are wholly or partiallyunresponsive, pixels with a dark signal, highly non-linear pixels, orpixels with much noise or electrical instability.

One method to mend such is by checking a pixel signal with all or partof the other signals in its proper column. If the deviation isconsidered spurious, the pixel is removed. Against random noise events,a certain column-wise averaging will reduce such effects. Non-idealdefects in the internal die structure can depend on developing anexpected performance metric and rejecting pixels that deviate too muchfrom the metric in question. Examples of such metric are the average,mean, minimum, maximum, or any low-pass filtered derivation from thepixel signals of the same column. Furthermore, admitted, i.e.non-rejected pixels can be subjected to low-pass filtering, such asaveraging to reduce random noise.

Now, the present invention has hereabove been disclosed with referenceto preferred embodiments thereof. Persons skilled in the art willrecognize that numerous modifications and changes may be made theretowithout exceeding the scope of the appended Claims. In consequence, theembodiments should be considered as being illustrative, and norestriction should be construed from those embodiments, other than ashave been recited in the Claims.

1. A method of using a line-scan sensor device to scan an image, thedevice comprising sensor cells arranged in a matrix of rows and columns,the method comprising: determining when a pixel signal value from apixel in a first row and in a column deviates from a composite valuecomposed from pixels in plural other rows and all in said column; andremoving the pixel signal value of the pixel in the first row and insaid column when the pixel signal value from the pixel in the first rowand in said column deviates from the composite value composed frompixels in plural other rows and all in said column, wherein the pixel inthe first row and in said column images a portion of the image and eachof the pixels in plural other rows and all in said column images thesame portion of the image.
 2. A method of using a plural-line imagesensor device according to claim 1, the method further comprisingreplacing the pixel signal value from the pixel in the first row and insaid column with a column-wise filtered pixel signal value comprised ofthe composite value composed from pixels in plural other rows and all insaid column.
 3. A sensor comprising: a plural-line image sensor deviceoperable to scan an image, the device comprising sensor cells arrangedin a matrix of rows and columns; and a processor operable to determinewhen a pixel signal value from a pixel in a first row and in a columndeviates from a composite value composed from pixels in plural otherrows and all in said column, and to remove the pixel signal value of thepixel in the first row and in said column when the pixel signal valuefrom the pixel in the first row and in said column deviates from thecomposite value composed from pixels in plural other rows and all insaid column, wherein the pixel in the first row and in said columnimages a portion of the image and each of the pixels in plural otherrows and all in said column images the same portion of the image.
 4. Asensor according to claim 3, wherein the processor is further operableto replace the pixel signal value of the pixel in the first row and insaid column with a column-wise filtered pixel signal value comprised ofthe composite value composed from pixels in plural other rows and all insaid column.
 5. A processor readable medium comprising plural modulesfor controlling a processor, the modules comprising: a module operableto control the processor to determine when a pixel signal value from apixel in a first row and in a column of a plural-line image sensordevice operable to scan an image deviates from a composite valuecomposed from pixels in plural other rows and all in said column; and amodule operable to control the processor to remove the pixel signalvalue of the pixel in the first row and in said column when the pixelsignal value from the pixel in the first row and in said column deviatesfrom the composite value composed from pixels in plural other rows andall in said column, wherein the pixel in the first row and in saidcolumn images a portion of the image and each of the pixels in pluralother rows and all in said column images the same portion of the image.6. A processor readable medium according to claim 5, wherein the modulesfurther comprise a module operable to control the processor to replacethe pixel signal value from the pixel in the first row and in saidcolumn with a column-wise filtered pixel signal value comprised of thecomposite value composed from pixels in plural other rows and all insaid column.